Re: [fpc-pascal] Timer in X11
On Thu, 22 Dec 2011, Graeme Geldenhuys wrote: On 21 December 2011 18:06, Henry Vermaak wrote: embedded devices, laptops have batteries, too. You're wasting CPU and power just spinning around a loop, so even if your app isn't active, it's still waking up every 50ms. I don't consider this very good programming practice. I'm always interested in improvements. The 50ms code was done purely to implement the Application.OnIdle() event. How else can I implement an OnIdle event then? I think it depends on what you mean with 'OnIdle'. - An event which occurs once when an application falls Idle. - An event which is triggered repeatedly when the application is idle. As I understand it, Delphi and Lazarus implement the former, and don't need a timeout for it. Michael.___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thu, Dec 22, 2011 at 9:15 AM, wrote: > As I understand it, Delphi and Lazarus implement the former, and don't need > a timeout for it. Ops, you are correct, it is a one shot event: http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/delphivclwin32/Forms_TApplication_OnIdle.html I think I implemented it as a repetitive event. ops =D I guess I'll need to fix this. But you should not try to compare directly the LCL gtk2 or qt4 widgetsets with fpgui since gtk2 and qt4 do most of the real work. Lazarus now has a X11 interface which can be used for direct comparisons and it uses the timeout. In general I don't fully trust select() to wakeup correctly yet. I guess that more testing would show if it does, but I read in the web that X11 could use more then one file descriptor for communication, so if I use a infinite select() the application could hang in some corner cases. -- Felipe Monteiro de Carvalho ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 22 December 2011 10:15, wrote: > > I think it depends on what you mean with 'OnIdle'. > - An event which occurs once when an application falls Idle. > - An event which is triggered repeatedly when the application is idle. fpGUI's OnIdle event used to fired only once, when the application goes idle - but I found it much more useful to have an idle event that fires repeatedly. Maybe I should make it configurable via the fpgApplication instance, so the developer can decide how they want it to work. -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thu, 22 Dec 2011, Felipe Monteiro de Carvalho wrote: On Thu, Dec 22, 2011 at 9:15 AM, wrote: As I understand it, Delphi and Lazarus implement the former, and don't need a timeout for it. Ops, you are correct, it is a one shot event: http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/delphivclwin32/Forms_TApplication_OnIdle.html I think I implemented it as a repetitive event. ops =D I guess I'll need to fix this. But you should not try to compare directly the LCL gtk2 or qt4 widgetsets with fpgui since gtk2 and qt4 do most of the real work. Lazarus now has a X11 interface which can be used for direct comparisons and it uses the timeout. In general I don't fully trust select() to wakeup correctly yet. Strange statement. If select() didn't do its job correctly, neither Qt or Gtk could do their job, or any network related program, for that matter. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 21 December 2011 16:53, Felipe Monteiro de Carvalho wrote: > not alone here using FPC, so I shamelessly stole code from fpgui, The joys of open-source software. :-) -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thu, 22 Dec 2011, Graeme Geldenhuys wrote: On 22 December 2011 10:15, wrote: I think it depends on what you mean with 'OnIdle'. - An event which occurs once when an application falls Idle. - An event which is triggered repeatedly when the application is idle. fpGUI's OnIdle event used to fired only once, when the application goes idle - but I found it much more useful to have an idle event that fires repeatedly. Maybe I should make it configurable via the fpgApplication instance, so the developer can decide how they want it to work. Well, the latter will consume CPU cycles, as indicated by others... It all depends on what the programmer needs. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thu, Dec 22, 2011 at 9:51 AM, wrote: > Strange statement. > > If select() didn't do its job correctly, neither Qt or Gtk could do their > job, or any network related program, for that matter. It is not about select working or not, it is about how many file descriptors X uses to communicate: http://fixunix.com/xwindows/91558-xconnectionnumber-select.html#post301681 I don't have time in the foreseeable future to find in which wierd corner case XAddConnectionWatch is necessary and test that a implementation which I come up with works, but Qt could pay someone to stay all week testing wierd corner cases and find the most perfect algoritm. For me, timeouting every second is already more then good enough, it could even be each half second. Already at 50ms I could not see my application with top in the top 20 CPU users (most of which were using zero), so I seriously doubt the battery usage concerns unless someone really measures it. -- Felipe Monteiro de Carvalho ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 21 December 2011 18:26, Felipe Monteiro de Carvalho <...> wrote: >> just spinning around a loop, so even if your app isn't active, it's still >> waking up every 50ms. I don't consider this very good programming practice. > > I tested with top and it doesn't even show my application in the top > 20 users of CPU. I was just about to mention that, and would have been very surprised if it did show CPU usage. I have always been careful with CPU usage in fpGUI's event loop. > It now adjusts the interval acoording to the installed timers, up to a > maximum of 1 second. Initially I thought that sounded like a good idea - but doesn't in now do even more processing that without the GetSmallestTimerInterval() function? Doing the timer loop, a math comparison for each timer etc. But realistically it should still hardly register as a blip in the CPU usage, so I guess it should be fine - especially if only one or so timers are ever used in a application. -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 22/12/11 09:15, Felipe Monteiro de Carvalho wrote: It is not about select working or not, it is about how many file descriptors X uses to communicate: http://fixunix.com/xwindows/91558-xconnectionnumber-select.html#post301681 I don't have time in the foreseeable future to find in which wierd corner case XAddConnectionWatch is necessary and test that a I already mentioned this, but perhaps you didn't read it. You don't need to test _any_ corner cases, that's the point of XAddConnectionWatch. You get a callback that gives you a file descriptor which you can add/remove to the descriptors you check with select(): http://groups.google.com/group/comp.windows.x/browse_thread/thread/cd32588d173fffcf/4b750082b055422b?q=mity&rnum=5&hl=en#4b750082b055422b algoritm. For me, timeouting every second is already more then good enough, it could even be each half second. Already at 50ms I could not see my application with top in the top 20 CPU users (most of which were using zero), so I seriously doubt the battery usage concerns unless someone really measures it. Perhaps you should try powertop. Henry ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thursday 22 of December 2011 09:43:28 Felipe Monteiro de Carvalho wrote: > On Thu, Dec 22, 2011 at 9:15 AM, wrote: > > As I understand it, Delphi and Lazarus implement the former, and don't > > need a timeout for it. > > Ops, you are correct, it is a one shot event: > > http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate > 2/EN/html/delphivclwin32/Forms_TApplication_OnIdle.html > > I think I implemented it as a repetitive event. ops =D I guess I'll > need to fix this. > > But you should not try to compare directly the LCL gtk2 or qt4 > widgetsets with fpgui since gtk2 and qt4 do most of the real work. > Lazarus now has a X11 interface which can be used for direct > comparisons and it uses the timeout. In general I don't fully trust > select() to wakeup correctly yet. I guess that more testing would show > if it does, but I read in the web that X11 could use more then one > file descriptor for communication, so if I use a infinite select() the > application could hang in some corner cases. FYI, qt and gtk2 uses same source for timers and loops - glib2. http://en.wikipedia.org/wiki/GLib http://developer.gnome.org/glib/2.26/glib.html I would try with it before reinventing wheel, because it works on all X11 platforms (even on OS/2 and BeOS) and I'm pretty sure that it's installed by default. zeljko ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] inline and other modifiers
On 22 Dec 2011, at 02:27, nore...@z505.com wrote: Another thing freepascal allows is for OVERLOAD to be declared one place but not the other. Delphi is more strict in this regard. That's fixed in svn trunk. Also delphi is more strict when it comes to PROGRAM name parsing. In freepascal the program name can mismatch the file name, whereas delphi stops compiling and tells you error. As Waldo Kitty mentioned, that's incorrect. And both FPC and Delphi require that unit names match the file name (except in case the FPC parameter -Un is used, and FPC also allows partial matches based on the first 8 characters of the unit/file name to accomodate 8.3 file systems). Another thing I noticed is you can just use a begin and end for freepascal without PROGRAM declaration at the top of the program.. again less strict than delphi. Delphi also allows that. Even gpc allows it, although it prints a warning. Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 22 Dec 2011, at 10:39, Graeme Geldenhuys wrote: On 21 December 2011 18:26, Felipe Monteiro de Carvalho <...> wrote: I tested with top and it doesn't even show my application in the top 20 users of CPU. I was just about to mention that, and would have been very surprised if it did show CPU usage. I have always been careful with CPU usage in fpGUI's event loop. Power usage is not only related to how much cpu power you use. Repeatedly waking up the cpu for minor processing also consumes more power than letting letting it stay in a low-power power saving mode. Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] using exceptions
On Wed, Dec 21, 2011 at 10:29 PM, wrote: > Marcos wrote: >> I use Exceptions to check the integrity of classes. I have one >> Exception for each class (E), most of the time. > > > Another problem with errors is that sometimes it is hard for a class to > return errors. In procedural programming you can usually return an error > as a parameter but sometimes in class programming it is difficult for > classes to just return errors. It's not difficult, but is boring have always a parameter or function return to return an error, and have to verify if error then... if not error... if error and error then... etc > Exceptions are an attempt to solve the problem, but imo this still doesn't > solve all problems and our applications are full of wild exceptions going > off despite our attempts to solve the problem.. because people fail to > check exceptions and catch them. usually I see code like this: > > Try > > Finally > > > You don't see as much Try Except, it's more Try Finally. People ignore the > exceptions because it's an accepted thing to do. Then the end user of the > application gets a strange exception message instead of a user friendly > one. For example, if a file is not found, I like to give a polite "Cannot > find file" message.. but usually in delphi apps and examples all over the > newsgroups you see just an EFileNotFound exception pop up instead. Or, > with StrToInt, a similar obscure exception message to the end user instead > of a more friendly one. I use many try-except in my own code but, most of the time, just catch my own exceptions because they are much more simpler to use. As I said before, I have Exceptions in only 2 levels: user and Lib (API, business rules, etc). The User exceptions always show a user friendly message (I think that you call Errors, right?). The Lib exceptions, for me, is the real Exception. So, If I call a routine but the app is not connected on DBMS... raise Exception; if a important property not been set... raise Exception; if a file has not found, this is not a exception, but if the app can not create a file... raise Exception. Marcos Douglas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On 22 December 2011 11:50, Henry Vermaak wrote: > > Perhaps you should try powertop. Thanks for this. I never knew about powertop. I just ran it for a few minutes. A fpGUI base app in idle rates 6th in the "top causes for wakeups" on my system - rated at 4% of total processes running. I have no idea how that relates to actual power usage though. My USB trackball (at 18%) and Firefox (at 16%) rated 2nd and 3th, respectively. The kernel_scheduler got the number one spot with 20+% share of all running processes. I don't think fpGUI is doing too badly, but also not ideal. I'll see if I can improve that code in fpGUI a bit. -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Timer in X11
On Thu, Dec 22, 2011 at 11:04 AM, zeljko wrote: > I would try with it before reinventing wheel, because it works on all X11 > platforms (even on OS/2 and BeOS) and I'm pretty sure that it's installed by > default. Interresting, but I don't think it will be necessary ... in rev 34359 I commited support for XAddConnectionWatch =D And I also don't like very much gnome APIs, although it could be added as an alternative via ifdefs if someone wants to go down this path. But I could not fix OnIdle to adere to the Delphi specification because that would affect assync call handling since there is only an TApplication.Idle event which handles both. LCL-Gtk2 fires OnIdle like a machine gun in a program with a timer, and I don't know if this is correct or not, it would be good if someone with Delphi could test. If it isn't correct or ideal then maybe we need a TApplication.PartialIdle (called by Idle too to keep compatibility) to handle things like AssynCall. I don't know where the hint update belongs to, PartialIdle or Idle The 1 second timeout needs to be kept anyway, because another thread could queue an assync call, so we need to check that periodically. -- Felipe Monteiro de Carvalho ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Contributed units on freepascal site
The contributed unit section on the freepascal site does not work anymore. Can someone please have a look and fix this? Is there an alternative link available? Regards, Darius ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
On 22 Dec 2011, at 14:37, dhkblas...@zeelandnet.nl wrote: The contributed unit section on the freepascal site does not work anymore. Can someone please have a look and fix this? Is there an alternative link available? The location of the page changed, and there's an "alternative" link available on the front page of http://www.freepascal.org under "Contributed units". Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
On 22 December 2011 15:40, Jonas Maebe wrote: > > The location of the page changed, and there's an "alternative" link > available on the front page of http://www.freepascal.org under "Contributed > units". While we are there. The "Toolbox" sponsor logo on the right. The Toolbox Magazine has been sold long ago to a new publisher. The "toolbox magazine" as we knew it, doesn't exist any more... they don't publish Pascal/Delphi related articles any more. Is that logo still needed on the free pascal website? -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
On 22 dec '11, Jonas Maebe wrote: > On 22 Dec 2011, at 14:37, dhkblas...@zeelandnet.nl [1]wrote: > >> The contributed unit section on the freepascal site does not work anymore. Can someone please have a look and fix this? Is there an alternative link available? > > The location of the page changed, and there's an "alternative" link available on the front page of http://www.freepascal.org [2] under "Contributed units". Well, that is exactly the link I'm talking about. Clicking on this link will open an new page, the title is shown, but no information. The browser shows an error occurred on the page. Webpage error details User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E; .NET CLR 1.1.4322; InfoPath.2) Timestamp: Thu, 22 Dec 2011 13:52:30 UTC Message: Expected identifier, string or number Line: 365 Char: 7 Code: 0 URI: http://www.freepascal.org/contrib/contribs.js [3] Message: 'fpWeb' is undefined Line: 23 Char: 5 Code: 0 URI: http://www.freepascal.org/contrib/contribs.html [4] Regards, Darius Links: -- [1] mailto:dhkblas...@zeelandnet.nl [2] http://www.freepascal.org [3] http://www.freepascal.org/contrib/contribs.js [4] http://www.freepascal.org/contrib/contribs.html ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
On 22 December 2011 15:40, Jonas Maebe wrote: > > The location of the page changed, and there's an "alternative" link > available on the front page of http://www.freepascal.org under "Contributed > units". Something else. The new page looks nice, but you can't select text and do copy-and-paste? Also I think somebody might need to go through that info and see what doesn't exist any more. I just randomly picked one, "File manager with sources in FPC". Can't copy and past any of the description text. Also the link http://fc.freepascal.org/ doesn't exist - I just get a "the connection has timed out" error in my browser. There are many more like this. -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
In our previous episode, dhkblas...@zeelandnet.nl said: > > > > The > location of the page changed, and there's an "alternative" link > available on the front page of http://www.freepascal.org [2] under > "Contributed units". > > Well, that is exactly the link I'm talking about. > Clicking on this link will open an new page, the title is shown, but no > information. The browser shows an error occurred on the page. It worked fine for me in Mozilla, but after I saw your user-agent, I tried MSIE (9.0) and while I don't get any error messages, nothing shows. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
In our previous episode, Graeme Geldenhuys said: > > The location of the page changed, and there's an "alternative" link > > available on the front page of http://www.freepascal.org under "Contributed > > units". > > While we are there. The "Toolbox" sponsor logo on the right. The > Toolbox Magazine has been sold long ago to a new publisher. The > "toolbox magazine" as we knew it, doesn't exist any more... they don't > publish Pascal/Delphi related articles any more. Is that logo still > needed on the free pascal website? The swpat logo also seems to be outdated and brings you to a general FFII page. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Contributed units on freepascal site
On 22 December 2011 16:00, Marco van de Voort wrote: > > It worked fine for me in Mozilla, but after I saw your user-agent, I tried > MSIE (9.0) and while I don't get any error messages, nothing shows. I can confirm that it works with Opera, Firefox and Chrome browsers. -- Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://fpgui.sourceforge.net ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] FPC for ARM
2011/12/19 Marco van de Voort > FreeBSD and Linux x86 and x86_64 have internal assembler, but not linker. > Though the FreeBSD/x86_64 internal assembler is only enable in trunk afaik. > > Be careful with binutils on ARM though, there are multiple ABIs, and the > installed ones must match the device. > I ran "apt-get install binutils" in the already installed Ubuntu and it worked. I have understood ARM also supports many instruction sets like Thumb and Thumb-2. I have no idea which one is running now, but it is not important because it works. Thanks for help. Is there an embedded web-server that would run on the ARM machine? Juha ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] FPC for ARM
In our previous episode, Juha Manninen said: > I ran "apt-get install binutils" in the already installed Ubuntu and it > worked. > I have understood ARM also supports many instruction sets like Thumb and > Thumb-2. > I have no idea which one is running now, but it is not important because it > works. > Thanks for help. > > Is there an embedded web-server that would run on the ARM machine? Afaik most ARMs simply run httpd/apache. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] using exceptions
On 12/22/11, nore...@z505.com wrote: > You don't see as much Try Except, it's more Try Finally. People ignore the > exceptions because it's an accepted thing to do. Then the end user of the > application gets a strange exception message instead of a user friendly > one. For example, if a file is not found, I like to give a polite "Cannot > find file" message.. but usually in delphi apps and examples all over the > newsgroups you see just an EFileNotFound exception pop up instead. Or, > with StrToInt, a similar obscure exception message to the end user instead > of a more friendly one. I tend to spend more time on catching errors and displaying user friendly and useful error messages than I do on writing the core functionality of most of my (simple) programs. Bart ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] using exceptions
Marcos Douglas: > It's not difficult, but is boring have always a > parameter or function return to return an error, > and have to verify if error then... if not er- > ror... if error and error then... etc If you mean having to write nested IFs to check all the errors, then there are several ways to make the error-checking in several calls "linearized": http://www.digipedia.pl/usenet/thread/1169/284/ I prefer using GOTO statements: begin Result := false; // Success flag [...] errMsg := errorOne; if not procOne (...) then GOTO ERROR; errMsg := errTwo; if not procTwo (...) then GOTO ERROR; errMsg := errThree; if not procThree(...) then GOTO ERROR; [...] Result := true ERROR: end This way, the funtion returns an error flag and a correspoinding message, and I prefer it to throwing and catching Exceptions. I even wrap exception- based code using external libraries in such proce- dures to have an easier and cleaner error handling. Also see: http://www.theregister.co.uk/2006/01/11/exception_handling/ Anton ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] using exceptions
On Thu, Dec 22, 2011 at 4:17 PM, Anton Shepelev wrote: > Marcos Douglas: > >> It's not difficult, but is boring have always a >> parameter or function return to return an error, >> and have to verify if error then... if not er- >> ror... if error and error then... etc > > If you mean having to write nested IFs to check all > the errors, then there are several ways to make the > error-checking in several calls "linearized": > > http://www.digipedia.pl/usenet/thread/1169/284/ No, I mean is better use try-except than nested IFs/GOTO/etc. > I prefer using GOTO statements: > > begin > Result := false; // Success flag > [...] > errMsg := errorOne; > if not procOne (...) then GOTO ERROR; > errMsg := errTwo; > if not procTwo (...) then GOTO ERROR; > errMsg := errThree; > if not procThree(...) then GOTO ERROR; > [...] > Result := true > ERROR: > end > > This way, the funtion returns an error flag and a > correspoinding message, and I prefer it to throwing > and catching Exceptions. I even wrap exception- > based code using external libraries in such proce- > dures to have an easier and cleaner error handling. > > Also see: > > http://www.theregister.co.uk/2006/01/11/exception_handling/ Thanks for the tips... but, IMHO, the code above would be more simpler like that: begin Result := False; // Success flag [...] procOne; procTwo; procThree; [...] Result := True; except on e: Exception do ShowMessage(e.Message); end; end; Marcos Douglas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Forward declarations
Can anyone think of a situation in which you would *have* to use forward declared functions? I'm trying to come up with an example for such for my book, and I am drawing a blank. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
Am Thursday 22 December 2011 21:33:13 schrieb Timothy Groves: > Can anyone think of a situation in which you would *have* to use forward > declared functions? I'm trying to come up with an example for such for > my book, and I am drawing a blank. > ___ > fpc-pascal maillist - fpc-pascal@lists.freepascal.org > http://lists.freepascal.org/mailman/listinfo/fpc-pascal procedure fwproc; forward; procedure myprocedure; begin fwproc; end; procedure fwproc; begin end; ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
Am 22.12.2011 21:37, schrieb Rainer Stratmann: > procedure fwproc; forward; > > procedure myprocedure; > begin > fwproc; > end; > > procedure fwproc; > begin > > end; Bad example, in this case there is no need for implementing fwproc after myprocedure. g Michael ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
On Thu, 22 Dec 2011 15:33:13 -0500 Timothy Groves wrote: > Can anyone think of a situation in which you would *have* to use forward > declared functions? I'm trying to come up with an example for such for > my book, and I am drawing a blank. Traverse a html tree. For example with div and p nodes. Both div and p nodes can have children that are div and p nodes. procedure Proc(RootNode: TNode); procedure ReadChildrenv(Node: TNode); forward; procedure ReadP(Node: TNode); begin ... ReadChildren(Node); end; procedure ReadDiv(Node: TNode); begin ... ReadChildren(Node); end; procedure ReadChildren(Node: TNode); begin for Child in Node do begin if Child is Div then ReadDiv(Child) else if Child is P then ReadP(Child); end; end; begin ReadChildren(RootNode); end; Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
Timothy Groves:
> Can anyone think of a situation in which you would
> *have* to use forward declared functions? I'm
> trying to come up with an example for such for my
> book, and I am drawing a blank.
Pascal User Manual and Report says:
Procecure (function) identifiers may be used be-
fore the procedure (funtion) declaration if
there is a forward declaration. Forward decla-
rations are necessary to allow mutually recur-
sive procedures and functions that are not nest-
ed. The form is as follows:
procedure Q(X:T); Forward;
procedure P(Y:T);
begin
Q(A)
end;
procedure Q;
{ parameters and result types are not repeated }
begin
P(B)
end;
But are "mutually recursive procedures and func-
tions" necessary?
Anton
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Re: [fpc-pascal] Forward declarations
Timothy Groves wrote: Can anyone think of a situation in which you would *have* to use forward declared functions? I'm trying to come up with an example for such for my book, and I am drawing a blank. Classic recursive-descent parser? An expression is a sequence of terms, a term is a sequence of factors, one of the possibilities for a factor is a parenthesised expression. However, there's probably still a way round that in a unit, by moving the first mention of one of those into the definition part. Or similarly you might be able to avoid it by using object definitions. -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
On 11-12-22 04:15 PM, Mark Morgan Lloyd wrote: However, there's probably still a way round that in a unit, by moving the first mention of one of those into the definition part. Or similarly you might be able to avoid it by using object definitions. Absolutely. Because in both of those cases, you've already declared the procedure forward. However, this section of the book is covering only ISO Pascal. I will be covering more advanced Pascal implementations (especially FPC) later on, but for the beginning section, I will be assuming no access to such. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
On 11-12-22 04:04 PM, Anton Shepelev wrote: But are "mutually recursive procedures and functions" necessary? Not at all. But there is no other reason to use forward-declared procedures that I can think of, and I need *something* to demonstrate why you might need them. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
Am Thursday 22 December 2011 22:04:34 schrieb Anton Shepelev: >Fward decla- >rations are necessary to allow mutually recur- >sive procedures and functions that are not nest- >ed. Forward declarations are the only option in special situations: If your program is huge and you only have this option to go on. Later you can clean up step by step the code. I search my project but didn't find a forward declaration anymore (so I did my homework). But I am sure that at some point it was necessary. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
You could apply the same logic to the Pascal "label" statement. You can (and should) always use a different construct and you could therefore claim that the "label" statement is unnecessary because you cannot think of a situation where there is no alternative - but it exists. And sometimes it is convenient to use. You could even go further and say that the multiplication operator is unnecessary because you can always achieve the same thing through repeated summation. But, of course, it is more convenient to use multiplication. Forward declared procedures exist in Jensen and Wirth Pascal and they exist for the purpose of allowing the convenience of those who sometimes find it easier or clearer to code an algorithm using mutual recursion. Why do you need a deeper explanation? Tony Whyman MWA Software On 22/12/11 21:24, Timothy Groves wrote: > On 11-12-22 04:04 PM, Anton Shepelev wrote: >> But are "mutually recursive procedures and functions" necessary? > Not at all. But there is no other reason to use forward-declared > procedures that I can think of, and I need *something* to demonstrate > why you might need them. > ___ > fpc-pascal maillist - fpc-pascal@lists.freepascal.org > http://lists.freepascal.org/mailman/listinfo/fpc-pascal ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
On 12/22/11 5:21 PM, Tony Whyman wrote: > [explanation snipped] Why do you need a deeper explanation? He is not asking for an explanation. (I think he knows what it is and can see why it might be useful.) He is asking for a compelling example as a use case that illustrates the need for this language construct. I haven't seen one in any replies yet. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Darwin i386 socket polling
I'm needing to figure out how socket signaling mechanisms work under darwin. Windows and Linux work, Darwin however does not support ePoll. Anyone have any experience with Sockets events under OSX i386? Thanks. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Forward declarations
Timothy Groves schrieb: Can anyone think of a situation in which you would *have* to use forward declared functions? I'm trying to come up with an example for such for my book, and I am drawing a blank. Well, maybe this one: --- type SorterProcType = function (String1,String2 : shortstring) : boolean; function CompareIt1(String1,String2 : shortstring) : boolean; forward; function CompareIt2(String1,String2 : shortstring) : boolean; forward; function CompareIt3(String1,String2 : shortstring) : boolean; forward; const SortCriteria : SortProcType = CompareIt1; --- I don't know of another way that you can use one of the "CompareIt1/2/3" functions in the const declaration for "SortCriteria" (but maybe there is one). ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
